Field of the Invention
This specification relates to a backlight unit using quantum dot phosphors, and more particularly, a backlight unit for realizing high efficiency and a display device having the same.
Background of the Invention
A backlight unit serves to emit light to a rear surface of a liquid crystal panel such that an image can be viewed by a user. Since the liquid crystal panel is unable to emit light by itself, the backlight unit should evenly emit light onto the rear surface of the liquid crystal panel, such that the user can visually recognize an image output on a display device. The backlight unit is provided with multiple light sources. With the development of technologies, light-emitting diodes (LEDs) have started to be used for the backlight unit, which replace cold cathode fluorescent lamps (CCFLs). The LED has many advantages, as compared with the CCFL, in view of less power consumption, an extended lifespan, a facilitated fabrication in a small size and the like.
There may be several methods of generating white light in a backlight unit using the LED as the light source. A representative method of generating white light may be a combination of light emitted from LEDs which emit blue light, red light and green light, respectively. However, this method requires too many LEDs and an additional feedback system, causing an increase in the fabrication costs of a display device.
Another method of generating white light may be a combination of an LED which emits blue light and yellow (YAG) phosphors. This method only requires about one third (⅓) of the LEDs employed in the combining method of the blue, red and green light emitting LEDs, and does not need the feedback system, thereby saving fabricating costs of a display device. However, this method has limited color reproduction.
To overcome such limitations, a method of replacing the conventional yellow phosphors with quantum dots (QD) has recently been reported. The quantum dots (QD) have different properties than typical phosphors. The quantum dots have a property of emitting different wavelengths of light depending on a type of material and a size of a particle. For example, quantum dots emit short wavelengths of light when particles are small in size, and emit long wavelengths of light when the particles become large in size. Therefore, by adjusting the size of the quantum dots, light with desired wavelengths from infrared to ultraviolet regions can be obtained.
The quantum dot phosphors are excited by primary light supplied from light sources to emit secondary light which has a different wavelength from the primary light. Here, the primary light refers to light supplied from the light sources, namely, light which excites the quantum dot phosphors. The secondary light refers to light emitted from the quantum dot phosphors.
To emit sufficient secondary light, a sufficient amount of quantum dot phosphors is required. However, an increase in the amount of the quantum dot phosphors raises the unit cost of a product. Thus, the increase in the amount of the quantum dot phosphors is not economically preferable and it also increases the size of the product. Therefore, if it is possible to generate white light by using a smaller amount of quantum dot phosphors, the unit cost of the product and the size of the product may be reduced.
In order to generate the white light with a relatively smaller amount of quantum dot phosphors, the primary light should be fully scattered. When the primary light is scattered, a path length of the primary light may increase and accordingly the white light can be generated by a smaller number of quantum dot phosphors, which may result in improved efficiency of the quantum dot phosphor.
Scattering particles are required for scattering the primary light. However, conventionally known scattering particles scatter even the secondary light emitted from the quantum dot phosphors, as well as the primary light supplied from the light sources. The scattering particles known in the related art can increase the efficiency of the quantum dot phosphors to some degree by increasing a content of the scattering particles. However, when the content of the scattering particles exceeds a predetermined level, the scattering particles may interfere with the extraction of the secondary light, which ends up lowering the efficiency of the quantum dot phosphors.